Recovery of ferric chloride and ferric oxide from iron chloride solutions

ABSTRACT

Finely divided coal or solid coal derivatives containing pyrite are reacted with a ferric ion solution; FeCl3 is particularly suitable. The ferric ion is reduced to ferrous ion and free sulfur is formed. The solution is then filtered from the coal which is then washed and heat dried under low pressure. Most of the free sulfur is volatized from the coal due to the heat drying; additional free sulfur can be removed by additional washing and heat drying and/or solvent extraction techniques. At least 60% of the pyrite sulfur and pyrite iron is removed using the process of this invention. If desired, the ferrous chloride can be regenerated; this permits iron oxide to be recovered as a byproduct.

United States Patent [191 Meyers Nov. 18, 1975 [54] RECOVERY OF FERRIC CHLORIDE AND 3,682,592 8/1972 Kovacs 423/140 FERRIC OXIDE FROM IRON CHLORIDE FOREIGN PATENTS OR APPLICATIONS SOLUTIONS 306,691 2/1929 United Kingdom 423/633 [75] Inventor: Robert A. Meyers, Encino, Calif. [73] Assignee: TRW Inc., Redondo Beach, Calif. '7 Examiiqerosc ar Vemz. Assistant Examiner-Brian E. Hearn Flledi 1973 Attorney, Agent, or FirmWillie Krawitz; Daniel T. [21] APP] 411,140 Anderson; Alan D. Akers Related US. Application Data [57] ABSTRACT [60] $8;f sggfggg g zg gs g} Finely divided coal or solid coal derivatives containing 19 197l Pat 3 768 988 u y pyrite are reacted with a ferric ion solution; FeCl is particularly suitable. The ferric ion is reduced to fer- 52 us CL 423 423 423 4 rous ion and free sulfur is formed. The solution is then 1 l 4 filtered from the coal which is then washed and heat [5]] Int 2 C016 49/10, C016 49/06 dried under low pressure. Most of the free sulfur is [58] Field of Search 423/493 6 633 150 volatized from the coal due to the heat drying; addi- 3 6 tional free sulfur can be removed by additional washing and heat drying and/or solvent extraction tech- [56] References Cited niques. At least 60%, of the pyrite sulfur and pyrite iron is removed using the process of this invention. If UNITED STATES PATENTS desired, the ferrous chloride can be regenerated; this 2 pennits iron oxide to be recovered as a byproduct. U 5011 2,592,580 4/1932 Loevenstein 423/633 1 Claim, 2 Drawing g r s 21 2o F el s I S I is e 3 WATER SOLUTION PRECIPITATION RENE VAPORIZATION l ATMAT I TATiM ATM ZIZF 55e 2|ZF I t Q Q 22 23 8 l S fiifiim F L $521!: N sia iianon Fezos FeCl MAKE-UP 00 com. l' FIL T kATION U.S. Patent Nov. 18, 1975 Sheet 1 GT2 3,920,791

H20 0 H2O T 2| I 20 I I9 5 S S Fec'3 Fec'z WATER SOLUTION PRECIPITATION A RIZAT. N REHEAT BY COOLING Y O I ATM l ATM 0 2|2F 55F T Q Q 22 23 I i I FeClg F Cl OXIDATION e 3 NR I ATM SOLUTION I? I; EEE T I N -'eCl MAKE-UP COAL &1? FILTRATION 'i Fig. 1

U.S. Patent Nov. 18, 1975 Sheet 2 of 2 c WASH H2O FOUR STAGE COAL WASHING 3 3 l2 l3 n4 :5

SULFUR COOLING MEDIA l8 SULFUR 2 CONDENSATION 225 F I6 I l7 COAL SULFUR (:P' DRYING VAPORIZATION l ATM ATM COAL 2l2F 450F Fig. 2

RECOVERY OF FERRIC CHLORIDE AND FERRIC OXIDE FROM IRON CHLORIDE SOLUTIONS BACKGROUND OF THE INVENTION This application is a continuation-in-part of application Ser. No. 116,262 filed Feb. 17, 1971 now abandoned, and a division of Ser. No. 163,893, filed 7/19/71, now US. Pat. No. 3,768,988. This invention relates to the removal of pyritic sulfur from coal and solid coal derivatives and more specifically to the solvent extraction of sulfur from pyrites in coal using a solution containing a ferric ion.

The present use of coal in the United States is primarily for the purpose of conversion into electrical energy and thermal generating plants. One of the principal drawbacks in the use of United States mined coal is due to their high sulfur contents which can range up to 5%.

Based on a 4% sulfur content, a 1 million kilowatt plant burns about 8500 tons per day of coal and consequently emits 6 tons per day of sulfur dioxide. If this sulfur could be removed and converted, it would produce 900 tons of H SO daily.

It has long been recognized that $0 in the atmosphere will either retard growth or kill vegetation. In addition, the potential hazard to humans appears about the same as for the vegetable kingdom.

While it is possible to remove pyritic sulfur from coal by froth floation or washing processes; these are not selective so that a large portion of the coal is discarded along with ash and pyrite. Hence, the solution so far has been to simply burn coal having a low sulfur content. However, many pollution control districts now prohibit the use of coal having an excess of 1% sulfur. The result has been to severely restrict the use of many U.S. coals, 90% of which average about 2.5% contained sulfur. This has lead to the importation of low sulfur content fuel oils for domestic and industrial use. The crude oil reserves, which are the source of the residue, are expected to run out in 30 years while coal reserves are sufficient for several hundred years at a minimum.

It is, therefore, an object of this invention to provide a process for the reduction of sulfur, particularly pyritic sulfur in coal.

Another object is to provide a process for the recovery from coal of sulfur and sulfur compounds.

Another object is to provide a process for recovery of iron values from coal containing pyrite.

Other objects of this invention will become apparent from the description and the diagram to follow.

According to the invention, it has been found that it is possible to react the pyrite contained in the coal with a solution containing an effective amount of ferric ion to obtain a high yield of free sulfur. Fe ion particularly as FeCl is preferred; other ferric ammonium sulfate, etc., may be employed. A typical reaction proceeds as follows: 2 FeCl FeS 3F eCl 25. The solution containing some free sulfur, ferrous chloride and any unconsumed ferric chloride is removed from the coal by filtration.

The coal is then washed and dried, preferably by heating in a vaccum; this results in the major portion of free sulfur being volatized as follows: S.Coal S coal. If desired, a further wash, filtration and heating will remove more of the sulfur and any residual ferrous ion. One or more extractions with a suitable organic sulfur solvent such as benzene, kerosene or para cresol 2 may be employed to further reduce the sulfur content of the coal.

Regeneration of the unused ferric chloride and ferrous chloride solution may be accomplished by first concentrating the solution by evaporating most of the water. The concentrated solution is cooled, thereby precipitating the ferrous chloride from the ferric chloride, most of the latter still remaining in solution. The precipitated ferrous chloride is air oxidized to ferric chloride and iron oxide and finally the ferric chloride is recycled and the iron oxide recovered.

Typical treatment temperatures may vary from 50-l10C. Reflux times are typically /22 hours and higher. Typical coal particle sizes may vary from 200 mesh to /a-inch pieces. Atmospheric pressure may be employed, but higher pressures can also be used.

The effective amount of the ferric ion solution employed for extraction depends on the amount of coal treated and its pyritic sulfur content, the amount of sulfur desired to be extracted, extraction times, extraction temperatures, concentration of the ferric ion in the solution, etc.

The reaction of ferric chloride and ferrous persulfide to produce free sulfur is known. However, it was unexpected that the reaction with ferric ion (e.g., FeCl and pyrite could be carried out in a coal medium since pyrite is dispersed very finely throughout the coal matrix, and penetration of such an organic matrix with water is known to be difficult. Furthermore, the volatization of sulfur from coal is unusual since it well might be expected that the free sulfur would recombine either with iron or with the coal upon heating. It is also well known that iron pyrites may be oxidatively dissolved from the coal matrix with strong aqueous oxidizing agents such as HNO H 0 or HOCl. This will convert the sulfur content to sulfate, but not to free sulfur. This is the basis for chemical analysis of the pyritic sulfur content of coal; however, such strong oxidizing agents also extensively oxidize the organic coal matrix. By contrast, ferric salts are almost totally selective in the sense that the organic coal matrix is undisturbed. Hence, ferric salts, but not HNO H 0 or HOCl, provide an economical route to the removal of pyrites from coal.

Coals which may be employed in this invention include those which are considered as coals in the popular or commercial sense, such as anthracites, charcoal, coke, bituminous coals, lignites, etc. In addition, chars from hydrocracked coals and middlings are all capable of being refined by the extraction process of this invention.

The invention will be understood by reference to FIGS. 1 and 2 in which ferric chloride make-up solution and coal are fed into a pyrite reactor 10 maintained at atmospheric pressure and about 212F. Pyrite (FeS is extracted from the coal, and the slurry containing unreacted ferric chloride, ferrous chloride, sulfur, ferrous persulfide, and the treated coal are fed to a coal filtration unit 11. Vacuum disk filters in the coal filtration unit are used to separate the bulk of the iron chloride solution from the treated coal.

In the coal washing sections 12, l3, l4, and 15, four stages of countercurrent washing with intermediate filtration steps are used to reduce the residual chloride content of the coal to less than about ppm. A suitable residence time of the coal in each of the washing stages is about 15 minutes; rotary vacuum disk filters are used to separate the coal and wash the solution be- 3 tween washing stages.

The washed coal is then fed to a coal drying unit 16 where rotary steam tube dryers are employed to remove the residual water from the washed coal, this opreactor 20, is transferred to an air oxidation furnace 22 where it is reoxidized back to ferric chloride and iron oxide, the reaction equation being FeC1 3/2 O- 4FeC1 +Fe2O The reaction employs air and is eration being carried out at atmospheric pressure and 5 carried out at atmospheric pressure at about 480F. about 212F. The heated dry coal is then forwarded to The oxidized precipitate (ferric chloride and iron oxa sulfur vaporization unit 17 where free sulfur, which ide) is then transferred to a solution-filtration unit 23 was produced in the extraction reaction in reactor 10, where the soluble ferric chloride is then separated from is vaporized at atmospheric pressure and a temperature the insoluble iron oxide by dissolving in water. The ferof about 450F or under reduced pressure (30 min.) ric chloride solution is recycled to the ferric chloride and at 250350F. The vaporized sulfur is removed by make-up solution for use in reactor 10. The iron oxide nitrogen gas into a sulfur condensation unit 18 and is filtered from the ferric chloride solution and may be cooled to about 225F causing it to condense. The sulrecovered as a byproduct of the process. fur vapor is then passed to a recovery unit as bright sul- Typical coals which may be employed in the process fur. The treated coal with reduced pyrite content is include Missouri, Lower Freeport, Bevier, Indiana No. then forwarded for use. V, and Pittsburgh. These coals contain sulfur forms as In the ferric chloride regeneration stage, the filtrate shown in Table 1 when freshly mined. As they stand exfrom the coal filtration unit 11 is passed to a thickener posed to air, small amounts of sulfate sulfur are formed unit 19 where water is vaporized from the solution at from the pyrite content.

TABLE 1 SULFUR COMPOUNDS IN COAL Lower Bevier Freeport Indiana No. V Pittsburgh Pyritic s 1.7 2.3 2.2 3.8 1.5 1.8 0.5 1.7 Organic 5 1.7 2.3 0.4 0.8 1.5 1.8 0.5 0.7 Total 5 3.5 4.5 3.0 4.2 3.0 3.5 1.2 2.2

atmospheric pressure and about 212F. The concentrated solution is then passed to a precipitation unit 20 where ferrous chloride is precipitated by cooling the solution to 155F at atmospheric pressure. Unreacted ferric chloride solution from the precipitation unit 20 is heated in a reheater 21 and then combined with ferric chloride make-up for feeding to the reactor 10.

The ferrous chloride precipitate, which has been separated by filtration from the ferric chloride solution in Table 2 shows the original pyritic sulfur content of the Missouri and Lower Freeport coals and the reduction in sulfur content due to treatment of FeCl- It will be observed that a marked reduction in pyritic sulfur occurs after only a single treatment with FeCl followed by a water washing and drying.

Table 3 shows the effect of employing an organic solvent to remove the free sulfur which remains following the FeCl and water washing treatment.

TABLE 2 FeCl EXTRACTION DATA Wt Loss Reflux After Sul- Sam Wt Molar- (9 0C) Washing fur Wt% Pyritic ple Coal Vol. ity 2Fe+3 Time & Drying Eschka Fe Sulfur Coal No. Grms I-eCl FeCl PyriticFe (hrs.) Wt7c WW: in Coal Removed Missouri Untreated 4.75 1.65 (Mesh Size -200) Missouri 1 200 0.5 3.9/1 16 0.22 (Mesh Size -200) 0.17 Missouri 2 500 0.3 5/1 2 9.1 4.18 0.86 3l/t (Mesh Size -200) 4.17 0.84 Missouri 3 30 500 0.5 13/1 20 +2.0 3.67 0.19 62% (Mesh Size -2(l0) 3.65 0.19 Lower Freeport U. 3.54 3.16 (Mesh Size -14) 3.99 3.52 Lower Freeport 4 50 730 0.5 6/1 2 l4.l 1.99 1.10 /z (Mesh Size l4) 'ASTM D271 -Bureau of Mines procedure and Standard Methods of Chemical Analysis. Furman. Volume 1. page 542. Remarks: Residue removed from condenser was analyzed by electron microprohe as follows: Fe. S. Si, O. C were major constituents; Ca. C1. A1 were trace.

Yellow cr formed; Hg spot test for free S was positive.

Sample 2 as washed once with 250 cc hot water and dried 24 hours in a C vacuum oven. Samples 3 and 4 were washed twice with 250 cc hot water and dried 72 hours at 90C in a vacuum oven.

TABLE 3 SOLVENT EXTRACTION DATA FOLLOWING FeCL, TREATMENT AND WATER WASH TABLE 3-continued SOLVENT EXTRACTION DATA FOLLOWING FeCl TREATMENT AND WATER WASH Sulfur Concentration From the data in Table 3, it appears that the organic solvent treatment causes a major portion of the pyritic sulfur to be extracted; also, use of para cresol appears to result in extraction of organic as well as pyritic bound sulfur. While the efficiencies shown range from 60% to at least 89%, this efficiency range can be changed by altering such factors as wash times, particle size, amounts and concentrations of FeCl and solvents, ferric salt treatment, reflux temperature, etc.

Table 4 shows the effect of FeCl extraction on various coals employing reaction conditions similar to Table 2. The table shows that 72-93% of the pyritic sulfur content may be removed in 2 hours by 0.5 M FeCl solution from a wide variety of coals. Further, the process was applicable to all the coals, and in the case of Indiana No. V, the extraction efficiency was excellent.

"All coals were 1 4 mesh except Bevier which was -200 mesh The process of this invention is extremely efficient in that at least 60% of the pyrite sulfur is extracted and the iron employed for extraction is easily recovered (about -90%) and may be reused. Furthermore, iron removal is facilitated since the iron contained in the FeCl extraction solution and the iron in the pyrite are indistinguishable; hence, no special techniques are required to separate different metals from the washextraction operation if metal recycling is desired.

in addition, the process is simple in that no high temperatures, pressures or catalysts are required.

Finally, the extraction with FeCl does not produce an interaction with the organic coal matrix; this permits substantially all of the coal to be utilized as low sulfur fuel.

What is claimed is: I

1. A process for recovering iron values from an aqueous solution containing ferric chloride and ferrous chloride ion which comprises:

concentrating the aqueous solution by water vaporization; Y

cooling the solution thereby precipitating the ferrous chloride at about F; separating the ferrous chloride precipitate from the solution containing ferric ion; v

oxidizing the ferrous chloride precipitate with air to ferric chloride and iron oxide at about 480F and 1 atmosphere;

dissolving the ferric chloride precipitate in water; and

separating the iron oxide from the aqueous solution containing the ferric chloride.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3,920,791

DATED November 18, 1975 |NVENTOR(5) I Robert A. Meyers It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, Line 29: After froth, "floatation" should read flotation.

Column 1, line 55: After ferric, insert the following which. was omitted salts such as acetate, nitrate, sulfate, citrate, oxide ferrous-.

Signed and fic'alcd this twentieth Day of April1976 [SEAL] A Hes t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnmissiuncr uj'larenls and Trademarks 

1. A PROCESS FOR RECOVERING IRON VALUES FROM AN AQUEOUS SOLUTION CONTANING FERRIC CHLORIDE AND FERROUS CHLORIDE ION WHICH COMPRISES: CONCENTRATING THE AQUEOUS SOLUTION BY WATER VAPORIZTION; COOLING THE SOLUTION THEREBY PRECIPITATING THE FERROUS CHLORIDE AT ABOUT 155*F; SEPARATING THE FERROUS CHLORIDE PRECIPITATE FROM THE SOLUTION CONTAINING FERRIC ION, OXIDIZING THE ERROUS CHLORIDE PRECIPITATE WITH AIR TO FERRIC CHLORIDE AND IRON OXIDE AT ABOUT 480*F AND 1 ATMOSPHERE DISSOLVING THE ERRIC CHLORIDE PRECIPITATE IN WATER; AND SEPARATING THE IRON OXIDE FROM THE AQUEOUS SOLUTION CONTAINING THE FERRIC CHLORIDE. 